Natural convection in an air filled enclosure with a localized nonuniform heat source mounted centrally on the bottom wall is numerically investigated. The vertical walls are cooled while the top wall and the remaining portions of the bottom wall are insulated. The heat source is assumed to be isothermal with a linearly varying temperature. The governing equations were solved using finite volume method on a uniformly staggered grid system. The computational results are presented in the form of isotherm and streamline plots and Nusselt numbers. The effects of the source nonuniformity parameter, lambda and the line source length, epsilon are investigated for the Grashof numbers Gr = 10(6) and 10(7). It is found that for Gr = 10(6) nonuniform heating of the line source enhances the overall heat transfer rate markedly compared to uniform heating of the heat source whereas for Cr = 10(7) its effect is marginal. (C) 2011 Elsevier Ltd. All rights reserved.